1. Field of the Invention
The present invention concerns an external fixation and immobilization device for a bone element or structure in particular a human member, especially adapted for use in the method known as the ILIZAROV method.
2. Summary of the Prior Art
It is known that this method, which is classical and widely used in orthopedic surgery fields, consists in associating, to a bone element or structure or to two parts of such structure, intersecting needles or pins, passing in pairs through the bone element or structure and supported in precisely defined positions by a kind of external open-worked housing, comprising two rigid metallic hoops or hoop portions, surrounding the bone element and separated from one another by brace elements having an adjustable length maintaining them in steady fixed position at a suitable distance, the needles or pins passing through the bone structure being dependent upon these hoops or half-ring portions and immobilized thereupon in order to cooperate with the bone element in two distinct, separated and perfectly localized zones. Advantageously, the pins or needles are engaged in the supports bone by the hoops and disposed so that they are oriented according to the radii of the hoops, these supports furthermore comprising means adapted to exert a tension or a compression upon these pins or needles in order to apply to the bone element a suitable strain.
According to certain embodiments already known in the prior art of such attachment devices utilized for carrying out the ILIZAROV method, especially for the kind of such as those described in U.S. patent application Ser. No. 830,654 dated Feb. 18, 1986 in the name of the present application for an external fixation device adapted for orthopedic use, it has already been foreseen, in particular to constitute hoops by means of a tube having a circular cross-section upon which are engaged articulated collars, provided with immobilization means to lock them in any given position on these hoops, certain of these collars furthermore comprising means adapted to receive and immobilize the ends of the pins or needles of which the opposite ends cooperate with the elements for submitting these pins to tension.
This solution, which offers various advantages, especially as to the simplicity of production and the fact that it comprises a reduced number of pieces necessary for its application, thus allowing to achieve a relatively precise positioning of the needles or pins with respect to the bone element to pass through, nevertheless presents drawbacks. In particular, in this solution, once the hoops are immobilized in position after adjustment of the length of their spacing braces, it is no longer possible to modify neither the orientation in azimuth of the crossing pins or needles, which remain radially oriented relative to the hoops nor their positioning in height, the fixation collars being directly intersected these pins or needles of which they are fastened.
Furthermore, due to the rounded cross-section of the hoops, the tightening of a collar on the hoops in order to immobilize it, does not always allow, under the effect of rotation torque created when a tension or compression strain is exerted on the pin or needle borne by the collar, to prevent the collar from turing on the hoop and shifting even slightly, the orientation of the corresponding pin or needle. Thus, this does not work properly and consequently this can be particularly prejudicial during reduction of a fracture or during treatment of a fracture by osteosynthesis.
The present invention concerns improvements proposed by a device for immobilizing a bone structure of element of this kind recalled herein-above, in particular of the type described in the above-mentioned U.S. patent application which, by overcoming the drawbacks of the solution described, offers complementary advantages to those already resulting from the structure thus envisaged.
According to the invention, the device concerned is characterized in that each hoop presents in cross section an external outline presenting two parallel flattened portions, connected respectively by two convex portions, the supports of the pins or needles borne by the hoops being constituted by lateral open blocks and presenting two wings comprising plane surfaces adapted to cooperate by plate sliding on the flattened portions of the hoop, these wings being associated by a concave portion matching the outline of one of the convex portions of the external outline of the hoop.
Due to these dispositions, the support blocks of the pins or needles interlock easily by the lateral side of the hoop intended to support them and, once placed in position, are no longer subjected to relative rotation around the corresponding hoop during the strains of these pins or needles, the plane bearing of the wings of the blocks on the flattened portions of the hoop preventing any shifting with respect to one another in the plane containing the pin or needle supported by the block.
According to one particular characteristic, each block mounted on a hoop comprises in one of its wings cooperating with one of the flattened portions of the hoop, a transversal bore, extending parallely to the flattened portion, internally threaded and within which is adapted to be driven a screw the end of which protrudes within a hole perpendicular to the bore, provided at the end of the wing of the runner and inside which is mounted a stop ball protruding from the end of this hole in order to issue through an opening having a smaller diameter delimited by a narrowing of the hole, so that the displacement of the screw ensures the blocking of the ball against the hoop and the immobilization of the runner.
According to another characteristic of the invention, at least one wing of each runner externally presents a tenon or a mortise, adapted to be respectively engaged in a mortise or tenon having the same outline, provided in a support comprising a passage crossed through by an externally threaded sleeve or sheath, itself axially provided with a narrow channel for the penetration of a pin or a needle locked with respect to the sheath, the support furthermore comprising a transversal housing in which is confined a nut cooperating with the external threaded part of the sheath whereas the passage of said sheath internally comprises a wedge or cleat sliding in axial groove provided in the external surface of the sheath, so that the rotation of the nut provokes the displacement of the sheath in the support and the putting under tension or compression with respect to the bone element of the corresponding pin or needle. According to a complementary characteristic, the pin or needle is locked in the narrow channel of the sheath by means of a screw engaged in a radial bore of a head corresponding to the end of the sheath.
According to another advantageous characteristic of the invention and in function especially of the particularly useful requirements of height adjustment of each support on one of the hoops of the device, each runner is associated to a wedge borne by one of the wings of the block, the correction between the wedge and the runner being achieved by means of an axis borne by the wedge and engaged in a bore provided in the wing of the runner, this bore extending perpendicularly to the flattened portions of the hoop. Preferably, the locking of the wedge with respect to the runner is carried out by a radial blocking screw, crossing a threaded hole provided in the body of the block and issuing into the passing bore of the shaft borne by the wedge. Usefully, the axis presents an intermediary groove into which penetrates the end of the blocking screw.
According to a further characteristic of the device of the invention, each hoop is advantageously constituted by means of the two half-hoops, adapted to be jointly associated by a set of two rectilinear extension pieces, of variable length in each set, presenting in straight cross-section an outline identical to that of the hoop, each extension piece comprising at its ends connecting members cooperating with the opposite ends of each half-hoop. Preferably, each connecting member is constituted by a protruding tip, borne of the half-hoop or the extension piece and penetrating within a housing of the same outline respectively provided in the extension piece of the half-hoop, the blocking of the extension piece and of the half-hoop after engagement of the tip in its housing being performed by at least one transverse screw.
According to yet another embodiment, each of the hoops is also associated to an assembly of double collars, each constituted by two pairs of jaws, connected by a common transverse axis, one of these pairs of jaws being adapted to tighten the hoop and the other end of an adjustable spacing brace, mounted between the two parallel hoops and extending perpendicularly at the plane of these hoops. Advantageously, each spacing brace is constituted by two parts disposed in the extension of one another and associated to an intermediary stretching device or turnbuckle, comprising a rod of which the two opposite ends are threaded in opposite directions and cooperate respectively with two nuts integral with the ends opposite the two parts of the spacing brace.
According to another particular characteristic, one of the two pairs of jaws of the double collar can be fastened to a bar comprising successive passages for the fixation of a pin or needle support, cantilevered with respect to the hoop.